Non-toxic mutants of pathogenic gram-negative bacteria

ABSTRACT

A method is provided for identifying, isolating, and producing htrB mutants of gram-negative bacterial pathogens. The method comprises mutating the htrB gene of a gram-negative bacterial pathogen so that there is a lack of a functional htrB protein, resulting in a mutant that lacks one or more secondary acyl chains contained in the wild type gram-negative bacterial pathogen, and displays substantially reduced toxicity as compared to the wild type strain. Also, the present invention provides methods for using a vaccine formulation containing the htrB mutant, the endotoxin isolated therefrom, or the endotoxin isolated therefrom which is then conjugated to a carrier protein, to immunize an individual against infections caused by gram-negative bacterial pathogens by administering a prophylactically effective amount of the vaccine formulation.

This invention has been made with government support under grant AI24616 awarded by the National Institutes of Health. The government hascertain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to compositions comprising alteredendotoxin (lipooligosaccharide (LOS); lipopolysaccharide (LPS)) ofgram-negative bacterial pathogens. More particularly, the presentinvention relates to the making of a form of endotoxin, by a geneticallyengineered gram-negative pathogen, which lacks a substantially toxiclipid A portion. Also disclosed are prophylactic and therapeutic uses ofthe substantially detoxified endotoxin, and of mutant gram-negativebacteria producing the substantially detoxified endotoxin.

BACKGROUND OF THE INVENTION

Gram-negative bacteria have an outer membrane comprised of componentsincluding proteins, lipoproteins, phospholipids, and glycolipids. Theglycolipids comprise primarily endotoxin-lipopoly-saccharides (LPS) orlipooligosaccharides (LOS), depending on the genus of bacteria. LPS aremolecules comprised of

a) a lipid A portion which consists of a glucosamine disaccharide thatis substituted with phosphate groups and long chain fatty acids in esterand amide linkages;b) a core polysaccharide which is attached to lipid A by an eight carbonsugar, KDO (ketodeoxyoctonoate), and heptose, glucose, galactose, andN-acetylglucosamine; andc) an O-specific side chain comprised of repeating oligo-saccharideunits which, depending on the genera and species of bacteria, maycontain mannose, galactose, D-glucose, N-acetylgalactosamine,N-acetylglucosamine, L-rhamnose, and a dideoxyhexose (abequose,colitose, tyvelose, paratose, trehalose). LOS has a similar structure asLPS, containing a lipid A portion and a complex carbohydrate structure,but differs in that it does not contain repeating O-side chains.

The major antigenic determinants of gram-negative bacteria are believedto reside in the carbohydrate structure of the O-specific side chain ofLPS and the complex carbohydrate structure of LOS. These carbohydratestructures may vary for different species of the same genera ofgram-negative bacteria by varying one or more of the sugar composition;the sequence of oligosaccharides; the linkage between theoligosaccharides; and substitutions/modifications of an oligosaccharide(particularly a terminal oligosaccharide).

LPS and LOS have been considered as bacterial components which havepotential as vaccine immunogens because of the antigenic determinants(“epitopes”) residing in their carbohydrate structures. However, thechemical nature of LPS and LOS prevent the use of these molecules invaccine formulations; i.e., active immunization with LPS or LOS isunacceptable due to the inherent toxicity of the lipid A portion. Thepathophysiologic effects induced (directly or indirectly) by lipid A ofLPS or LOS in the bloodstream include fever; leucopenia; leucocytosis;the Shwartzman reaction; disseminated intravascular coagulation;abortion; and in larger doses, shock and death. Accordingly, there areno currently available vaccines which induce antibody responses to LPSor LOS epitopes.

As shown in FIG. 1, the lipid A portion of endotoxin generally comprisesa hydrophilic backbone of glucosamine disaccharide which is eithermonophosphorylated or diphosphorylated (positions 1 and 4′); and whichcarries at least six molecules of ester- and amide-bound fatty acids.Four molecules of (R)-3-hydroxytetradecanoate (e.g. 3-hydroxy-myristoylor β-hyroxymyristic acid or β-OH) are linked directly to the lipid Abackbone at positions 2, 3, 2′, and 3′. Hydroxyl groups of two of thefour molecules of β-OH are substituted with normal fatty acids (termed“secondary acyl chains”, and including dodecanoate, tetradecanoate, andhexadecanoate) in forming acyloxyacyl groups.

One approach to making a detoxified endotoxin molecule involvesisolating the endotoxin, and enzymatically-treating the isolatedendotoxin with a human neutrophilic acyloxyacyl hydrolase (U.S. Pat.Nos. 4,929,604, 5,013,661 and 5,200,184). The acyloxyacyl hydrolasehydrolyzes the fatty acids (non-hydroxylated, secondary acyl chains)from their ester linkages to hydroxy groups of β-OH (hydroxylated). Theresultant altered endotoxin, from enzymatic treatment, contained a lipidA moiety lacking non-hydroxylated fatty acids. This altered endotoxinexhibited reduced in vivo toxicity, but retained antigenicity.

Another approach involves a method of modifying isolated endotoxin byselectively removing the β-OH that is ester-linked to the reducing-endglucosamine backbone at position 3 (U.S. Pat. No. 4,912,094;Reexamination B1 4,912,094). The selective removal of β-OH wasaccomplished using alkaline hydrolysis. The resultant modified endotoxinexhibited reduced in vivo toxicity, but retained antigenicity.

Both approaches involve chemically treating isolated endotoxin. Neitherapproach discloses the production in a gram negative bacterial pathogenof an endotoxin having substantially reduced toxicity, yet retainingantigenicity. Further, there has been no disclosure of the use of agram-negative bacteria, which has been engineered to produce anendotoxin having substantially reduced toxicity and yet retainingantigenicity, in a prophylactic or therapeutic vaccine against endotoxicshock and gram-negative bacteremia.

SUMMARY OF THE INVENTION

The present invention is directed to a method for producing, in a mutantgram-negative pathogen, LPS or LOS which exhibits substantially reducedtoxicity as compared to the wild type endotoxin, and which retains theantigenicity of its corresponding wild type endotoxin. The methodcomprises creating a mutation in the htrB gene of the gram-negativebacterial pathogen such that there is a lack of functional HtrB proteinin the mutated gram-negative bacterial pathogen. It was found that lipidA produced by the htrB mutant lacks one or both of the fatty acids(non-hydroxylated or secondary acyl chains) thereby rendering theendotoxin in an isolated form, or the mutant gram-negative bacterialpathogen bearing the endotoxin, substantially reduced in toxicity andyet retaining antigenicity, as compared to wild type. Endotoxin isolatedfrom htrB mutants, or the htrB mutants themselves (whole cell vaccine),can be used to immunize individuals at risk of gram-negative bacteremiaby inducing antibodies to the major antigenic determinants which residein the carbohydrate structure of the O-specific side chain of LPS andthe complex carbohydrate structure of LOS. Further, the htrB mutants canbe engineered to express heterologous antigens of other microbialpathogens at the surface of the htrB mutant for presentation to avaccinated individual's immune system in a multivalent vaccine. Also,the endotoxin isolated from the htrB mutants of the present inventionmay be used to generate LPS or LOS-specific antibody which may be usefulfor passive immunization and as reagents for diagnostic assays directedto detecting the presence of gram-negative bacterial pathogens inclinical specimens.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of the general structure of lipid Aof gram negative bacteria of the family Enterobacteriaceae.

FIG. 2A is a schematic representation of the general structure of aspecies of lipid A, from the LOS of an htrB mutant, comprising pentaacyldiphosporyl lipid A.

FIG. 2B is a schematic representation of the general structure of aspecies of lipid A, from the LOS of an htrB mutant, comprising tetraacyldiphosporyl lipid A.

FIG. 3 is a graph showing the relative toxicity of an htrB mutant (∘, Δ)as compared to wild type bacteria (□) in a TNFα release assay.

FIG. 4 is a photograph showing human primary respiratory epithelialcells unstimulated (control), exposed to NTHi 2019 LOS, or exposed tohtrB mutant B29 LOS, and reacted with either a fluorescent probe thathybridizes to TNFα mRNA (probe 1) or a fluorescent control probe (probe2).

FIG. 5 is a graph showing mean titers of anti-LOS antibody against NTHI2019 LOS (antigen coating) in ELISA from mice immunized with NTHi 2019(Pool 595), htrB mutant B29 LOS (Pool 597), or htrB mutant B29 LOSconjugated to a carrier protein (Pool 606), with adjuvant.

FIG. 6 is a graph showing the mean titers of anti-LOS antibody againsthtrB mutant B29 LOS (antigen coating) in ELISA from mice immunized withNTHi 2019 (Pool 595), htrB mutant B29 LOS (Pool 597), or htrB mutant B29LOS conjugated to a carrier protein (Pool 606), with adjuvant.

FIG. 7 is a schematic representation comparing the structures of wildtype Salmonella lipid A and htrB mutant lipid A.

DETAILED DESCRIPTION OF THE INVENTION Definitions:

“Endotoxin” is a term used herein for purposes of the specification andclaims to refer to the LPS or LOS of gram-negative bacterial pathogens,wherein the endotoxin is either in a cell-associated or isolated form.“htrB endotoxin” and “htrB mutant endotoxin” refer to endotoxin isolatedand purified from an gram-negative bacterial pathogen htrB mutant.

“vaccine candidate or vaccine antigen” is a term used herein forpurposes of the specification and claims to refer to an endotoxinepitope having one or more of the following properties (a-d): (a) isimmunogenic; (b) is surface-exposed (which can be shown by techniquesknown in the art including immunofluorescence assays, electronmicroscopy staining procedures, and by bactericidal assays); (c) inducesantibody having bactericidal activity in the presence of complementand/or functions in immune clearance mechanisms; (d) induces antibodywhich neutralizes other functional activity of the epitope(immunogenicity, or toxicity, etc.).

“Gram-negative bacterial pathogen” is a term used herein for thepurposes of the specification and claims to refer to one or morepathogenic (to humans or animals) bacterium of a genus and speciesincluding Neisaseria meningitidis, Neisseria gonorrhoeae, Haemophilusinfluenzae, Haemophilus ducreyi, other Haemophilus species, Moraxellacatarrhalis, Campylobacter jejuni, Salmonella typhimurium, otherSalmonella species, Shigella dysentariae, and other Shigella species,and Pseudomonas aeruginosa.

“Substantially reduced in toxicity” is a term used herein for thepurposes of the specification and claims to refer to a reduction inbioactivity of at least 10 fold to 100 fold or more as compared to wildtype endotoxin.

“Carrier protein” is a term used herein for the purposes of thespecification and claims to refer to a protein which is conjugated tothe htrB mutant endotoxin. While the htrB mutant endotoxin appears to beimmunogenic on its own, it is known in the art that conjugation to acarrier protein can facilitate immunogenicity. Proteins which may beutilized according to the invention include any protein which is safefor administration to mammals and which may serve as an immunologicallyeffective carrier protein. In particular embodiments, cell surfaceproteins, membrane proteins, toxins and toxoids may be used. Criteriafor safety would include absence of primary toxicity and minimal risk ofallergic reaction. Diphtheria and tetanus toxoids fulfill thesecriteria; that is, suitably prepared they are non-toxic, and theincidence of allergic reactions is acceptably low. Although the risk ofallergic reaction may be significant for adults, it is minimal forinfants.

According to additional particular embodiments of the invention,appropriate carrier proteins include, but are not limited to Salmonellaflagellin, Haemophilus pilin, Pseudomonas pili, Pseudomonas exotoxin,outer membrane proteins of Haemophilus (15 kDa, 28-30 kDa, and 40 kDamembrane proteins) or N. meningitidis or N. gonorrheae, Escherichia coliheat labile enterotoxin LTB, cholera toxin, pneumolysin of S.pneumoniae, and viral proteins including rotavirus VP7 and respiratorysyncytial virus F and G proteins. Additionally, there are many carrierproteins known in the art including, but not limited to, keyhole limpethemocyanin, bovine serum albumin, and diphtheria toxin cross-reactivemutant protein (“CRM”). Additionally, there are several methods known inthe art for conjugating endotoxin to a carrier protein. Such methods mayinclude, but are not limited to, the use of glutaraldehyde, orsuccinimidyl m-maleimidobenzoate, or1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide, or by usingbromoacetylated carrier protein (see, e.g. Robey et al., 1989, Anal.Biochem. 177:373-377). Conjugation of htrB endotoxin to a carrierprotein toxin may reduce toxicity of the carrier protein toxin, butresidual toxicity may remain. Further detoxification may be accomplishedby means known in the art such as employing formalin which reacts withfree amino groups of the carrier protein toxin.

Alternatively, native carrier protein toxin may be detoxified withformalin to produce a conventional toxoid before conjugation to the htrBmutant endotoxin. However, the prior formalin treatment reduces thenumber of free amino groups available for reaction during theconjugation process. CRM have an advantage in that they have no inherenttoxicity yet none of their amino groups are occupied by the formalin. Inthe case of CRM197, which is immunologically identical to native toxin,treatment with formalin (though there is no need to detoxify) greatlyenhances the immunological response. It is thought that this is due tostabilization of the molecule against degradation by mechanisms of thebody and/or aggregation by cross-linking (immunogenicity of particlesincreases with size). While tetanus and diphtheria toxins are desirablecarrier proteins, there may be other candidate carrier proteins whichmay also be suitable. Such other candidates for carriers include toxinsand proteins of pseudomonas, staphylococcus, streptococcus, pertussis,and E. coli.

Conjugation of endotoxin to carrier proteins can be performed by avariety of methods such as by direct conjugation to the carrier proteinby cyanogen bromide, reductive amination, or by using bifunctionallinkers. Such bifunctional linkers include, but are not limited to,N-hydroxy succinimide-based linkers cystamine, glutaraldehyde, anddiamino hexane. htrB endotoxin is modified to contain sulfhydryl groupswith the use of N-hydroxy succinimide-based linkers, or by the use ofcarbodiimide-mediated condensation of cystamine. Thesulfhydryl-containing htrB endotoxin intermediates are then reacted to acarrier protein that has been derivatized with N hydroxy succinimidylbromo acetate. Preferably, sulfhydryl groups are exposed on theconjugating htrB endotoxin for making a thiol linkage with thebromoacetylated carrier protein.

In a specific embodiment of the invention, htrB mutant endotoxin may beconjugated to a carrier protein, such as CRM, by using long chain sulfoN-succnimidyl 3-(2-pyridylthio)-propionate to thiolate the primary aminogroup(s) of the endotoxin. Long chain sulfo N-succnimidyl3-(2-pyridylthio)-propionate was added to approximately 13 mg of thesaccharide component of the htrB endotoxin in 0.1 M NaHCO₃ pH7.0 at aratio of 1:1 (w/w) and incubated for an hour at room temperature. Themixture is then purified by gel filtration. The long chain sulfoN-succnimidyl 3-(2-pyridylthio)-propionate derivatized fractions werepooled. The N-pyridyl disulfides present in the derivatized fractionswere reduced with 100 mM dithiothreitol, and purified by gel filtration.The thiolated endotoxin fractions were then collected. CRM197 wasbromoacetylated by adding bromoacetic acid N hydroxy succinimide in asmall volume of dimethyl formamide dropwise to CRM (in 0.1 M NAHCO₃) ata ratio of 1:1 (w/w) at 4° C. The solution was mixed and incubated for 1hour at room temperature. The reaction mixture was then purified by gelfiltration, and the fractions containing bromoacetylated protein werecollected. Derivatization of amino groups on carrier protein tobromoacetyl groups was monitored by a decrease in the amount of freeamino groups. Bromoacetyl CRM in 0.1 M NaHCO₃ was added to the thiolatedhtrB mutant endotoxin at a 1:1.5 ratio of protein to endotoxin (w/w) in0.1 M NaHCO₃/1 mM EDTA, and the reaction was incubated overnight at 4°C. The final conjugate was then be purified by gel filtration in aphosphate buffered saline pH 6.9.

The methods and compositions of the present invention relate to LPS andLOS biosynthetic pathways of gram-negative bacterial pathogens. Morespecifically, the present invention relates to mutations in the htrBgene of gram-negative bacterial pathogens resulting in mutant bacteriabearing endotoxin which is substantially reduced in toxicity, and yetretains antigenicity, as compared to wild type bacteria of the samespecies.

The genetics of lipid A biosynthesis of enteric bacteria, as it wasknown at the time of the present invention, is summarized in Schnaitmanand Klena (1993, Microbiol. Rev. 57:655-682). Genes lpxA, lpxB, lpxC,and lpxD encode gene products which function on the glucosamine backboneof lipid A including transfer of β-hydroxymyristic acid to glucosamine.The htrB gene was described as a gene that affects the inner corestructure (KDO, heptose, phosphorylethanolamine (PEA)) which wasdiscovered during a screen for genes necessary for growth of Escherichiacoli at elevated temperatures. Knockout mutations of htrB resulted inmutant E. coli which exhibited a reduced sensitivity to deoxycholate, aninability to grow at temperatures above 32.5° C., and a decrease in LPSstaining intensity (Schnaitman et al., 1993, supra; Karow et al., 1992,J. Bacteriol. 174:7407-7418). Karow et al. further noted that at betweenabout 30° C. to about 42° C., E.coli htrB mutants have changes in thefatty acid composition of both LPS and phospholipids, and particularly,overproduce phospholipids, as compared to wild type. However, it wasneither known nor suggested which one or more of the at least sixmolecules of ester- or amide bound fatty acids is lacking in the lipid Aportion of LPS of htrB mutants. Also no mention was made that htrBmutants contained a lipid A moiety specifically lacking one or bothnon-hydroxylated (secondary acyl chain) fatty acids responsible forendotoxicity; i.e. that the htrB mutant contained an altered endotoxinexhibiting reduced in vivo toxicity, but retaining antigenicity (“htrBendotoxin”), as compared to wild type.

The discoveries comprising the present invention include the unexpectedresults that knockout mutations of the htrB gene of gram-negativebacteria (including the family Enterobacteriaceae) result in htrBmutants which specifically lack one or more secondary acyl chain fattyacids which are ester-bound to the hydroxyl groups of two of the fourmolecules of β-OH (as shown in FIG. 2). Thus, it appears that the HtrBprotein has either acyltransferase activity, or indirectly or directlyaffects regulation of acyltransferase activity. The following examplesare presented to illustrate preferred embodiments of aspects of thepresent invention, and are not intended to limit the scope of theinvention. In particular, a preferred embodiment is the making of an H.influenzae htrB mutant, and methods of using the same as a whole cell,or to isolate therefrom the endotoxin, in vaccine preparations or togenerate antibodies for therapeutic or diagnostic applications. However,since the lipid A moiety is highly conserved among bacteria of thefamily Enterobacteriaceae and closely related gram-negative bacteria,the invention relates to gram-negative bacterial pathogens, as definedpreviously herein. There is microheterogeneity in terms of the length ofthe secondary acyl chain (12 or 14 carbon chains) and to which of thefour β-OH are substituted (1, 2, or 4) (Erwin et al., 1991, Infect Immun59:1881-1887); however, the nature of the substitution is the same andthus the particular steps (genes and gene products) involved in thebiosynthetic pathway appear conserved. For example, removal of secondaryacyl chains from various gram-negative bacterial pathogens (E. coli, H.influenzae, P. aeruginosa, S. typhimurium, and N. meningitidis) usinghuman acylxyacyl hydrolase resulted in deacylated LPS from all speciestested having significantly reduced mitogenic activity (Erwin et al.,1991, supra) as compared to the respective wild type strain.

EXAMPLE 1 Identification of an htrB Gene, and Generation of htrB Mutants

By complementing a nontypable H. influenzae strain 2019 with a S.typhimurium rfaE mutant strain, the rfaE gene of H. influenzae strain2019 was cloned (Lee et al., 1995, Infect Immun 63:818-824). Sequenceanalysis of the upstream region of the H. influenzae rfaE gene revealedan open reading frame highly homologous to the E. coli htrB gene. The H.influenzae htrB gene comprises 933 bases and encodes a protein, HtrB, of311 amino acids (SEQ ID NO:1) and an estimated molecular size of 36kilodaltons (kDa). Comparison of the deduced amino acid sequence of theH. influenzae HtrB with the E. coli HtrB revealed shared homology (56%identity and 73% similarity). Cloning the htrB gene of H. influenzaeinto a plasmid, and subsequent in vitro transcription-translationanalysis, revealed that HtrB has an apparent molecular size of 32-33kDa.

There are various standard techniques known to those skilled in the artfor mutating a bacterial gene. Those techniques include site-directedmutagenesis, and shuttle mutagenesis using transposons. In one aspect ofthis embodiment, mutagenesis of the htrB gene was carried out by shuttlemutagenesis. A derivative of the bacterial transposon Tn3, mini-Tn3(Seifert et al., 1986, Proc. Natl. Acad. Sci. USA 83:735-739), was usedas an insertion sequence to mutate the htrB gene. A 2.4 kilobase (kb)BglII containing the htrB gene from H. influenzae was cloned into aplasmid which was used as a target for mini-Tn3 transposon mutagenesis.Briefly, introduced into a single bacterial cell (E. coli), is theplasmid containing the htrB gene; a plasmid immune to Tn3 transpositionand containing transposase (which mediates the cointegration between Tn3and the target molecules); and a plasmid containing mini-Tn3.

After allowing for transposition, the bacterial cells are mated with anE. coli strain containing the cre enzyme that is used to resolvecointegrates in shuttle mutagenesis. Transconjugates were selected forwith antibiotics (kanamycin, ampicillin, and streptomycin) and analyzedby restriction endonuclease digestion.

Two plasmids, termed pB28 and pB29, each with a mini-Tn3 transposoncontaining the chloramphenicol acetyltransferase (CAT) gene insertedinto the htrB open reading frame at a different location. Each plasmidwas used to transform nontypable H. influenzae strain 2019 and bacterialcell transformants were selected for by growth in the presence ofchloramphenicol (1.5 μg/ml), resulting in identification of mutantstrains designated NTHi B28 and B29, respectively. Locations of the mTn3insertion in the chromosomes of the NTHi mutants were confirmed bygenomic Southern hybridization using the 2.4 kb BGlII fragment as aprobe. In particular, a BglII digest of NTHi strain 2019 DNA resulted ina 2.4 kb fragment; whereas similar digests of DNA from mutants NTHi B28and B29 revealed 4.0 kb fragments. Further, the 4.0 kb fragments weredigested by EcoRI which is present in the mTn3.

Alternatively, methods are known in the art to perform site-directedmutagenesis into a bacterial gene (See for example, Halladay, 1993, J.Bacteriol. 175:684-692), and recombination of the mutated bacterial geneinto the bacterial chromosome. A selectable kanamycin resistancecassette may be used to insert into, and mutate, the htrB gene containedwithin a shuttle plasmid. Subsequent transformation into a bacterialhost cell with the shuttle plasmid, and recombination of the bacterialgenome (at the site of the genomic copy of the htrB gene) with thecassette via htrB flanking sequences, results in the site-directedmutagenesis of the bacterial htrB gene.

Primer extension analysis can be used to determine the promoter regionof the htrB gene. The H. influenzae htrB's promoter region wasdetermined by primer extension analysis by first growing the bacteria,harvesting and purifying the RNA, and using a commercial primerextension kit according to the manufacturer's suggestions. A singletranscription site was found using a primer (SEQ ID NO:2) complementaryto the 5′ region of the htrB open reading frame. The first nucleotidewas a cytosine (C) residue located at 21 bp upstream of the putativetranslation start site, ATG. The region upstream of the transcriptionstart site contained a sequence (SEQ ID NO:1, bases 13 to 29) similar tothe consensus −10 region of the bacterial σ⁷⁰-dependent promoters at anappropriate distance. An element (SEQ ID NO:1, bases 1 to 6) resemblesthe consensus sequence of the −35 region.

EXAMPLE 2 Characterization of htrB Mutants Growth Characteristics

NTHi B28 and B29 strains were initially selected at 30° C., and wereunable to grow at 37° C. With further passages at 30° C. the NTHi htrBmutants began to lose temperature sensitivity and demonstrated a slowrate of growth, as compared to NTHi 2019, at 37° C. However, for growthtemperatures greater than or equal to 38.5° C., the temperaturesensitivity remained for the htrB mutants.

It was reported previously that E. coli htrB mutants demonstrated achange in membrane permeability to various compounds including kanamycinand deoxycholate (Karow et al., 1992, supra). The NTHi htrB mutants werealso tested for sensitivity to kanamycin and deoxycholate. Overnightcultures grown at 30° C. were then diluted and allowed to grow in thepresence of 5 μg/ml kanamycin at either 30° C. or 37° C. At 30° C., nodifference was detected in the growth rate between NTHi 2019 and theNTHi htrB mutant strains in the absence of kanamycin. However, thegrowth of the htrB mutants was significantly inhibited in the presenceof kanamycin, whereas NTHi 2019 was not affected. For the htrB mutants,the sensitivity to kanamycin was even greater at 37° C., since themutants failed to show growth in the presence of kanamycin at 37° C.Likewise, at 30° C. the htrB mutants showed sensitivity, as compared toNTHi strain 2019, at concentrations of greater than 500 μg/mldeoxycholate, and failed to grow at 1000 μg/ml. At 37° C., the htrBmutants showed almost complete inhibition of growth in the presence ofonly 250 μg/ml deoxycholate.

Endotoxin Characteristics

The LPS of E. coli htrB mutants has been characterized as being weaklystained on silver-stained polyacrylamide gels, but its migration patterndid not vary as compared to LPS from wild type. In contrast, the LOSfrom NTHi mutants B28 and B29 migrated faster than that from NTHi strain2019 on silver-stained gels. Additionally, the LOS from the B28 and B29mutants displayed a brownish color rather than black, as displayed byNTHi 2019. Reconstitution, by introducing a plasmid with an intact htrBgene into the mutant, of NTHi mutant B29 confirmed that the differencesin growth characteristics and LOS migration and staining were due tomutation of the htrB gene.

The NTHi htrB mutant LOS and wild type LOS were each analyzed byelectrospray ionization-mass spectrometry (ESI-MS) to provide molecularmass profiles for the different components of LOS. First, LOS wasisolated from the respective strains. LPS or LOS can be isolated by thephenol-water method (Westphal et al., 1965, Methods in CarbohydrateChemistry 5:83-91); or using an alternative purification procedure(using a protease; Hitchcock et al., 1983, J. Bacteriol. 154:269-277).The isolated LOS species were then O-deacylated by mild hydrazinetreatment (37° C. for 20 minutes; see Phillips et al., 1990, Biomed.Environ. Mass Spectrom. 19:731-745). Analysis by ESI-MS of the differentLOS species showed that while the O-deacylated LOS from NtHi mutant B29and NTHi 2019 were similar in molecular mass profile, two differencescan be clearly discerned. In the htrB mutant, there is a decrease (50%reduction) in the amount of LOS containing two phosphoethanolamines(PEA) in the inner core structure; and there is a shift to highmolecular weight LOS species containing more hexoses. These findingssuggest that the degree of phosphorylation may be affecting chainprogression from specific heptose moieties, and that HtrB eitherdirectly or indirectly affects phosphorylation of LOS.

Mass spectrometry was used to analyze the lipid A. More specifically,lipid A from htrB mutant LOS and from wild type LOS were each analyzedby liquid secondary ion mass spectrometry (LSIMS) in the negative ionmode to provide a spectrum of molecular ions for the differentcomponents lipid A. First, the LOS species were each hydrolyzed in 1%acetic acid for 2 hours at 100° C. at a concentration of 2 mg/ml. Thehydrolysates were centrifuged, and the supernatants removed. The watersoluble crude lipid A fractions were washed twice in water, and once inan organic mixture (chloroform/methanol/water; by volume 2:1:1) and thenevaporated to dryness. For analysis, the lipid samples were redissolvedin CH₂Cl₂/CH₃OH (3:1, v/v) and 1 μl ofnitro-benzylalcohol/triethanolamine (1:1, v/v) and applied as a liquidmatrix onto a mass spectrometer. LSIMS of the wild type (NTHi 2019)revealed a spectrum containing two deprotonated molecular ionsconsistent with a hexaacyl lipid A structure containing either one(hexaacyl monophosphoryl lipid A, M_(r)=1744) or two phosphates(hexaacyl diphosphoryl lipid A, M_(r)=1824). This spectrum isessentially identical to that reported for the lipid A structure of LOSof H. ducreyi (Melaugh et al., 1992, J. Biol. Chem. 267:13434-13439).The lower mass fragments are believed to be ions which arise throughLSIMS-induced fragmentation of higher ass mono- and diphosphorylatedmolecular ion species.

In contrast, the LSIMS spectrum for the lipid A preparation from thehtrB mutant LOS lacks molecular ions corresponding to the wild typehexaacyl lipid A species. There are two high mass ions which correspondto the molecular ions for a mono- and diphosphoryl pentaacyl lipid Aspecies missing one of the secondary acyl chains (e.g. myrisitic acidmoiety). Further, at the lower masses are two additional molecular ionspecies that correspond to a mono- and diphosphoryl tetraacyl lipid Aspecies lacking both secondary acyl chains. In summary, the lipid Astructure of the wild type's LOS is hexaacyl; whereas the lipid Astructure of the htrB mutant shows two species, a tetraacyl (FIG. 2A)and a pentaacyl species (FIG. 2B) indicating the loss of at least one,and sometimes both secondary acyl chains. The htrB mutant is comprisedof approximately 90% tetraacyl lipid A with only the fourhydroxymyristic acid ester and amide-linked fatty acids, andapproximately 10% pentaacyl lipid A with one myristic acid substitution.

EXAMPLE 3 Substantially Reduced Toxicity of htrB Mutants

The effect due to the lack of one or more secondary acyl chains on thetoxicity of a gram-negative bacterial pathogen was examined using astandard in vitro assay for measuring in vivo toxicity. Murinemacrophage-like cell line J774, when stimulated by endotoxin, secretesTNFα. The amount of TNFα, a directly proportional to the toxicity of thestimulating LPS or LOS, can be measured by (a) removing the cell-freesupernatant containing the TNFα; (b) adding the supernatant to aTNFα-sensitive cell line, such as WEHI 164; and (c) measuring theresultant cytotoxicity (See for example, Espevik et al., 1986, J ImmunolMethods 95:99; Sakurai et al., 1985, Cancer Immunol Immunother 20:6-10;Adams et al., 1990, J Clin Microbiol 28:998-1001; Adams et al., 1990, JLeukoc Biol 48:549-56; Tsai et al., 1992, Cell Immunol 144:203-16; andPfister et al., 1992, Immunol 77:473-6).

In this assay, adherent J774 cells were removed from culture, washedwith PBS-1 mM EDTA, and then washed twice with complete tissue culturemedium without antibiotics. 2×10⁶ to 4×10⁶ J774 cells/100 mm culturedish were incubated in tissue culture medium overnight in aCO₂,incubator. Adherent J774 cells are removed with PBS-1mM EDTA, washedthree times in tissue culture medium, and adjusted to 5×10⁵/ml. Aliquotsof 50 μl were added per well of a round bottom 96 well plate. The plateis then incubated for 1 hour at 37° C. in a CO₂ incubator. Per well isadded either an htrB mutant, or the wild type strain, in various colonyforming units (cfu, infection dose). The plate is then incubated at 37°C. for 1 hour in a CO₂ incubator. After the incubation, 100 μl ofculture medium containing 50 μg/ml gentamycin is added per well. Theplate is then incubated overnight at 37° C. in a CO₂ incubator. Aliquotsof 50 μl of the J774 supernatant were removed per well and transferredinto wells of a flat bottom 96 well plate. Serial 10 fold dilutions weremade of the J774 supernatant. Included as a control is a dilution seriesof recombinant TNFα (rTNFα). Added per well is 50 μl of WEHI 164 clone13 cells at 6×10⁵ cells/ml in tissue culture medium+25 mM LiCl+2 μg/mlactinomycin D; and the mixture was incubated overnight at 37° C. in aCO₂ incubator. After the incubation, 10 μl of alomar blue is added, and5-7 hours later the optical density is read at 570 nm. The assayutilizes alomar blue as a color indicator; i.e., alomar blue isconverted to a red color by living cells, but remains blue if the cellsare killed.

FIG. 3 shows a comparison between the number of bacterial cells of H.influenzae strain 2019 (wild type, □), and of bacterial cells of htrBmutant NTHi B29 (∘ and Δ) necessary to stimulate the release of enoughTNFα from J774 cells to kill the TNFα-susceptible cell line WEHI 164.B29_(hi) (Δ) and B29_(LO) (∘) refer to a high number (>3) and low number(<3) of passages of htrB mutant, respectively. As shown in FIG. 3, thehtrB mutant shows a reduced ability to stimulate TNFα release; i.e.,between an approximately 10 fold reduction (B29_(LO)) to anapproximately 100 fold reduction (B29_(hi)). This reduced ability tostimulate TNFα is one indication of the htrB mutant being substantiallyreduced in toxicity due to the lack of one or more secondary acyl chainsin the lipid A portion of the endotoxin.

The effect due to the lack of one or more secondary acyl chains on thetoxicity of a gram-negative bacterial pathogen was also examined using astandard in situ assay for measuring in vivo toxicity. SV-40 transformedhuman respiratory epithelial cells and human primary respiratoryepithelial cells, when stimulated by endotoxin, produces TNFα whichproduction can be demonstrated by detection of TNFα mRNA using methodsknown to those skilled in the art for in situ hybridization (amodification of MacNaul et al., 1990, J. Immunol. 145:4154-66). Thecells are grown in a mono-layer within wells of a 24-well plate untilapproximately confluent. To stimulate the cells, 1 μg/ml of LOS isadded, and the cells are incubated overnight at 37° C. A counterstain(e.g., membrane stain) is added and the cells are then fixed with 0.5 mlof 2% paraformaldehyde in buffer so that the counterstain is fixeddirectly into the cells. Hybridization is then performed using anoligonucleotide probe specific for TNFα RNA (SEQ ID NO:4), and a controlprobe (SEQ ID NO:5). The amount of TNFα mRNA visually detected isdirectly proportional to the toxicity of the stimulating LPS. TNFα mRNAwas minimally induced in SV-40 transformed human respiratory epithelialcells, and human primary respiratory epithelial cells (FIG. 4), exposedto LOS isolated from the htrB mutant NTHi B29. This is in contrast toLOS isolated from parent strain NTHi 2019 which induced high levels ofTNFα mRNA in these human respiratory cells (FIG. 4) and cell lines.

The substantial reduction in toxicity exhibited by the htrB mutant, asobserved by the TNFα assays, due to the lack of one or more secondaryacyl chains is further supported by previously reported assays ofbioactivity of endotoxin treated with acyloxyacyl hydrolase whichselectively removes the secondary acyl chains from endotoxin. Deacylatedendotoxin from E. coli, H. influenzae, N. meningitidis, and S.typhimurium were (a) similarly reduced in potency in the Limulus lysatetest relative to the respective wild type endotoxin; (b) reduced in theability to stimulate neutrophil adherence to human endothelial cellsrelative to the respective wild type endotoxin; and (c) reduced inmitogenic activity for murine splenocytes (Erwin et al., 1991, InfectImmun 59:1881-1887); yet maintained expression of antigenic epitopes.Similarly, S. typhimurium LPS treated with acyloxacyl hydrolase showed areduction in toxicity by 100-fold or greater in a dermal Shwartzmanreaction; was less pyrogenic in a thermal response model; showed a 5 to12 fold reduction in B-cell mitogenicity; and showed a 10 to 20 foldreduction in the release of prostaglandin E₂, as compared to wild typeendotoxin, in concluding that maximally deacylated LPS was at least 10fold less toxic than wild type endotoxin (U.S. Pat. No. 4,929,604).

EXAMPLE 4 Use of htrB Mutants as Immunogens

In one aspect of this embodiment, the htrB mutant of a gram-negativebacterial pathogen is used as a whole cell vaccine. The benefit of usinglive, attenuated (weakened in its ability to cause pathogenesis)bacteria as an immunogen in a vaccine formula is that they are able tosurvive and may persist in the human or animal body, and thus conferprolonged immunity against disease. In conjunction with the benefit ofusing a live bacteria to prolong the immune response, gram-negativebacterial pathogen htrB mutants have the added benefit in that theyexhibit substantially reduced toxicity. Another advantage, as comparedto a vaccine formulation comprising an isolated peptide representing abacterial antigen, is that a bacterial antigen expressed on the surfaceof a bacterial cell will often result in greater stimulation of theimmune response. This is because the surface of bacteria of the familyEnterobacteriaceae acts as a natural adjuvant to enhance the immuneresponse to an antigen presented thereon (Wezler, 1994, Ann NY Acad Sci730:367-370). Thus, using a live bacterial vaccine, such as an htrBmutant, to express complete proteins in an native conformation (i.e., aspart of the bacterial outer membrane) is likely to elicit more of aprotective immune response than an isolated protein alone.

Live bacterial vaccine vectors of the family Enterobacteriaceae thathave been described previously include attenuated Salmonella strains(Stocker et al., U.S. Pat. Nos. 5,210,035; 4,837,151; and 4,735,801; andCurtiss et al., 1988, Vaccine 6:155-160; herein incorporated byreference), and Shigella flexneri (Sizemore et al., 1995, Science270:299-302; herein incorporated by reference). One preferred embodimentis to provide a vaccine delivery system for human or animal (dependingon the genus and species of the gram-negative bacterial pathogen)mucosal pathogens. Thus, immunization by the parental route or by themucosal route with a prophylactically effective amount of the htrBmutant, or an htrB mutant transformed to recombinantly expressadditional bacterial antigens (that do not negatively affect the growthor replication of the transformed htrB mutant), can lead to colonizationof mucosal surfaces to induce mucosal immunity against the antigensdisplayed on the surface of, or secreted from the htrB mutant. Theresultant htrB mutant can be used in a vaccine formulation whichexpresses the bacterial antigen(s).

Similar methods can be used to construct an inactivated htrB mutantvaccine formulation except that the htrB mutant is inactivated, such asby chemical means known in the art, prior to use as an immunogen andwithout substantially affecting the immunogenicity of the expressedimmunogen(s). For example, human bronchial mucosal immunity has beenstimulated with an aerosol vaccine comprising lysed H. influenzae (Latilet al., 1986, J Clin Microbiol 23:1015-1021). Either of the live htrBmutant vaccine or the inactivated htrB mutant vaccine may also beformulated with a suitable adjuvant in order to further enhance theimmunological response to the antigen(s) expressed by the vaccinevector, as to be described in more detail.

In another aspect of this embodiment, the endotoxin is isolated from thehtrB mutant using methods known in the art, and the isolated htrBendotoxin is used in a vaccine formulation. As mentioned previously,major antigenic determinants of gram-negative bacteria are believed toreside in the carbohydrate structure of the O-specific side chain of LPSand the complex carbohydrate structure of LOS. However, the chemicalnature of LPS and LOS prevent the use of these molecules in vaccineformulations; i.e., active immunization with LPS or LOS is unacceptabledue to the inherent toxicity of the secondary acyl chains of the lipid Aportion of endotoxin. The endotoxin isolated from an htrB mutant of agram-negative bacterial pathogen lacks one or more secondary acylchains, and thus exhibits substantially reduced toxicity as compared toendotoxin isolated from the respective wild type bacteria. Therefore,endotoxin isolated from an htrB mutant of a gram-negative bacterialpathogen can be used in a vaccine formulation in inducing immunityagainst the respective wild type gram-negative bacterial pathogen. LPSor LOS can be isolated by the phenol-water method (Westphal et al.,1965, Methods in Carbohydrate Chemistry 5:83-91); or using analternative purification procedure (using a protease; Hitchcock et al.,1983, J. Bacteriol. 154:269-277).

Many methods are known for the introduction of a vaccine formulationinto the human or animal (collectively referred to as “individual”) tobe vaccinated. These include, but are not limited to, intradermal,intramuscular, intraperitoneal, intravenous, subcutaneous, ocular,intranasal, and oral administration. Conventionally, vaccineformulations containing either live bacteria, or attenuated orinactivated bacteria, are administered by injection or by oraladministration. For example, respiratory immunity can be stimulated byintestinal immunization with purified H. influenzae antigens (Cripps etal., 1992, J. Infect Dis 165S1:S199-201; herein incorporated byreference). The vaccine formulation may comprise a physiologicallyacceptable solution as a carrier in which the htrB mutant bacterialcells or isolated htrB mutant endotoxin is suspended. Various adjuvantsmay be used in conjunction with vaccine formulations. The adjuvants aidby modulating the immune response and in attaining a more durable andhigher level of immunity using smaller amounts of vaccine antigen orfewer doses than if the vaccine antigen were administered alone.Examples of adjuvants include incomplete Freund's adjuvant, Adjuvant 65(containing peanut oil, mannide monooleate and aluminum monostearate),oil emulsions, Ribi adjuvant, the pluronic polyols, polyamines,Avridine, Quil A, saponin, MPL, QS-21, and mineral gels such as aluminumhydroxide, aluminum phosphate, etc. The vaccine formulation isadministered in a prophylactically effective amount to be immunogenic,which depends on factors including the individual's ability to mount animmune response, the degree of protection to be induced, and the routeof administration.

In another aspect of the invention, the vaccine formulation can beadministered orally by including it as part of the feed given toeconomically important livestock. As known by those skilled in the art,species of Haemophilus, Campylobacter, Pseudomonas, and Salmonella arepathogenic for economically important livestock. Using the methodsaccording to the present invention, as illustrated in the followingexamples, htrB mutants of such animal pathogens can be produced. Theresultant htrB mutants, or endotoxin isolated therefrom, can be used ina vaccine formulation. Use of vaccine formulations, containing one ormore antigens of various microbial pathogens, in animal feed has beendescribed previously (See for example, Pritchard et al., 1978, Avian Die22:562-575).

EXAMPLE 5 H. influenzae htrB Mutants as Immunogens

In one embodiment, the htrB mutant is an H. influenzae htrB mutant.Haemophilus influenzae is an important human respiratory tract pathogenin diseases including otitis media, chronic sinusitis, and chronicobstructive pulmonary disease. Certain surface-exposed bacterialcomponents, including P2, P6, and LOS, appear to be antigens which mayconfer a protective immune response in immunized humans. Such antigenshave been shown to be targets of bactericidal antibody, and the presenceof serum bactericidal antibody is associated with protection frominfection by H. influenzae (Faden et al., 1989, J. Infect. Dis.160:999-1004).

5.1 In one aspect of the this embodiment, the endotoxin isolated from anhtrB mutant is used as the immunogen in a vaccine formulation. Asdemonstrated in Example 3 herein, the endotoxin isolated from an htrBmutant of a gram-negative bacterial pathogen lacks one or more secondaryacyl chains, and thus exhibits substantially reduced toxicity ascompared to endotoxin isolated from the respective wild type bacterialpathogen. Therefore, endotoxin isolated from an htrB mutant of H.influenzae can be used in a vaccine formulation in inducing immunityagainst the respective wild type strain. The htrB mutant LOS may beisolated by a method known to those skilled in the art for isolatingLOS. The htrB mutant LOS may be used in a vaccine formulation containingone or more agents selected from the group consisting of apharmaceutically acceptable carrier (e.g., a physiological solution), anadjuvant, or a carrier protein.

To illustrate the effects of immunization with htrB mutant LOS, a mousemodel was used. NTHi 2019 LOS, and htrB mutant NTHi B29 LOS were eachisolated from their respective strains using the phenol-water method.Groups of at least 5 Swiss Webster mice were immunized subcutaneouslywith 1 μg of either NTHi 2019, htrB mutant B29 LOS, or htrB mutantconjugated to a carrier protein, with adjuvant QS-21. Sera was collectedfrom each group 5 weeks after immunization, and the sera from animalscomprising a group were pooled. The pooled sera was assessed for titerof anti-LOS antibody by enzyme-linked immunosorbent assay (ELISA).Microtiter wells of ELISA plates were coated with either 10 μg of NTHi2019, or htrB mutant B29 LOS. FIG. 5 illustrates the mean titers ofanti-LOS antibody against NTHI 2019 LOS (antigen coating) in ELISA frommice immunized with NTHi 2019 (Pool 595), htrB mutant B29 LOS (Pool597), or htrB mutant B29 LOS conjugated to a carrier protein (Pool 606).FIG. 6 illustrates the mean titers of anti-LOS antibody against htrBmutant B29 LOS (antigen coating) in ELISA from mice immunized with NTHi2019 (Pool 595), htrB mutant B29 LOS (Pool 597), or htrB mutant B29 LOSconjugated to a carrier protein (Pool 606). Pre-immune sera was alsoincluded as a control (“week 0” or “time 0”).

The antibody induced by the different LOS preparations were then testedfor functional activity by performing bactericidal assays using NTHi2019 as the target. Into the wells of a 96-well plate are added 0.150 mlbuffer, 0.040 ml pooled human sera as a complement source, and 0.01 mlof NTHi 2019. Typically, the organism is plated in a dilution (e.g. 20to 200 cfu). Into test wells are added the respective antisera eitherundiluted (“neat”), 1/10 dilution, or 1/100 dilution. The plate is thenrotated vigorously (175-200 rpm) at 37° C. for 30 minutes. Aliquots fromrespective wells are plated on media and grown to determine percentagesurvival, and log kill. Log kill is calculated as the log(cfu 30minutes/cfu time 0). The results of the bactericidal assay are shown inTable 1, where Group R595 is the antisera induced by NTHI 2019 LOS,Group R597 is the antisera induced by htrB mutant B29 LOS, and GroupR606 is the antisera induced by htrB mutant B29 LOS conjugated to acarrier protein.

TABLE 1 Group week dilution % survival log kill R595 0 neat 1.00 −1.991/10 37.30 −0.43 1/100 87.20 −0.06 5 neat — −4.49 1/10 0.07 −3.15 1/10020.20 −0.70 7 1/10 — −4.62 1/100 7.80 −1.11 R597 0 neat 3.50 −1.46 1/1062.40 −0.20 1/100 108.60 0.04 5 neat — −4.49 1/10 4.40 −1.36 1/100 82.40−0.08 7 1/10 — −4.49 1/100 99.80 0.00 R606 0 neat 0.13/110.5 −2.87/0.921/10 130.20 0.11 1/100 106.50 0.03 5 neat 1.5/0.1  −1.81/−2.9 1/10 25.10−0.60 1/100 164.10 0.22 7 1/10 0.04 −3.44 1/100 185.90 0.27

The greater the log kill (the more negative the number, e.g. −4.49), thegreater the bactericidal activity is of the respective antibody. Thus,for comparison purposes, at week 7 and at a 1/10 dilution, log kill forthe antisera induced by NTHi 2019 LOS is −4.62, the log kill for theantisera induced by NTHi htrB mutant B29 LOS is −4.49, and the log killof the antisera induced by htrB mutant B29 LOS conjugated to a carrierprotein is −3.44. By ELISA, it looks like the antisera induced by htrBmutant B29 LOS antibody is low in titer; yet, as demonstrated by thebactericidal assays, significant functional antibody is raised byimmunization with htrB mutant B29 LOS.

5.2 In another aspect of the this embodiment, htrB mutant bacterialcells are used as the immunogen in a vaccine formulation. To illustratethe effects of immunization with htrB mutant bacterial cells, an infantrat model was used. The use of the infant rat model as a model ofbacteremic infections due to type b H. influenzae (Hib) in humans, andfor determining the virulence of type b H. influenzae strains, has beenaccepted by those skilled in the art (see, e.g., Smith et al., 1973,Infect. Immun. 8:278-290; Moxon et al., 1974, J. Infect. Dis.129:154-62; Rubin et al., 1983, Infect. Immun. 41:280-284; Zwahlen etal., 1985, J. Infect. Dis. 152:485-492).

Type b strain A2 of H. influenzae has already been characterized as ahighly virulent strain in the infant rat model system that causesbacteremia and meningitis after inoculation (e.g., intraperitoneal orintranasal), and as a clinical isolate from humans (it isolated from achild with meningitis due to H. influenzae). Using the methods accordingto Example 1, an htrB mutant was made from Hib strain A2. One week oldinfant Sprague-Dawley albino rats were inoculated intraperitoneally witheither 10⁷ Hib strain A2 or 10⁷ htrB A2 mutant and then assessed forintravascular clearance by measuring the number of colony forming units(cfus) per ml of blood obtained 48 hours post-inoculation. The resultsshowed that 20 of 20 infant rats inoculated with Hib strain A2 showedbacteremia, with all rats showing greater than 10⁵ cfu/ml of strain A2.In contrast, only 13 of 20 infant rats inoculated with htrB A2 mutantshowed bacteremia, with only 10 of the 13 showing greater than 10⁵cfu/ml of htrB A2 mutant.

Similarly, one week old infant Sprague-Dawley albino rats wereinoculated intranasally with either 10⁷ Hib strain A2 or 10⁷ htrB A2mutant and then assessed for intravascular clearance. The results showedthat 8 of 20 infant rats inoculated with Hib strain A2 showedbacteremia, with 7 of those 8 rats showing greater than 10⁵ cfu/ml ofstrain A2. In contrast, none of the 30 infant rats inoculated with htrBA2 mutant showed bacteremia. Taken together, it can be concluded fromthis model system that htrB mutants demonstrate attenuated virulence, ascompared to its wild-type strain, as indicated by the decreased abilityto cause bacteremia (e.g., a 30% reduction in the occurrence ofbacteremia).

To further illustrate the effects of immunization with htrB mutantbacterial cells, a chinchilla model was used. The use of the chinchillamodel as a model of middle ear infections due to nontypable H.influenzae (NTHi) in humans, and for determining the virulence of NTHistrains, has been accepted by those skilled in the art (see, e.g.,Bakaletz et al., 1989, Acta Otolaryngol. 107:235-243; Madore et al.,1990, Pediatrics 86:527-34; Barenkamp, 1986, Infect. Immun. 52:572-78;Green et al., 1994, Methods Enzymol. 235:59-68).

NTHi 2019 is a clinical isolate described previously (see, e.g., Murphyet al., 1986, Infect. Immun. 54: 774-779). Each healthly adultchinchilla was inoculated, via the epitympanic bulla into the middle earspace, with various log doses of either NTHi 2019 or htrB mutant NTHiB29. The course of middle ear disease was then assessed by periodicotoscopic examination for tympanic membrane inflammation or middle earinfusion, and aspiration from the middle ear with subsequent culture.The results showed that when compared to NTHi 2019, it takes up to a 3log greater dose of htrB mutant NTHi B29 (10⁷ cfu/ear) to induce middleear infection. It can be concluded from this model system that htrBmutants demonstrate attenuated virulence, as compared to its wild-typestrain, as indicated by the decreased ability to cause middle eardisease.

In another aspect of this embodiment the H. influenzae htrB mutant isgenetically engineered to express one or more heterologous bacterialantigens. As will be discussed in more detail below, H. influenzae has anatural genetic transformation process involving linearized DNA binding,uptake via one or more uptake sequences (e.g. AAGTGCGGT—SEQ ID NO:3),translocation, and recombination. Thus, one mechanism to introduce arecombinant DNA molecule containing the at least one heterologousbacterial antigen to be expressed, is to transform the host H.influenzae htrB mutant with linearized recombinant DNA moleculecontaining the DNA encoding the at least one heterologous bacterialantigen (“the encoding sequence”). Alternatively, the recombinant DNAmolecule containing the encoding sequence to be expressed can beinserted into a plasmid vector, and either introduced into as alinearized recombinant molecule by the natural transformation process;as circularized recombinant plasmid using electroporation ofnoncompetent H. influenzae htrB mutants; or as a circularizedrecombinant plasmid transformed into competent H. influenzae htrBmutants.

Plasmids useful for cloning of and expression from recombinant DNAmolecules in H. influenzae are known to those skilled in the art. Suchplasmids include:

pRSF0885 confers ampicillin resistance, and contains a PvuII cloningsite and a defective TnA sequence (Setlow et al., 1981, J. Bacteriol.148:804-811), and can replicate in both H. influenzae and E.coli (Trieuet al., 1990, Gene 86:99-102).pDM2 was constructed by cloning chloramphenicol resistance intopRSF0885; and pDM5 was constructed by cloning tetracycline resistanceinto pRSF0885 (McCarthy et al., 1986, J. Bacteriol. 168:186-191).pVT63, pVT64, pVT65, pVT66 are improved shuttle vectors for H.influenzae and E. coli based on pDM2 (Trieu et al., 1990, Gene86:99-102), and contain the pUC-derivative of the ColEl ori, and thepRSF0885 rep locus. Additionally, each plasmid has drug markers withunique restriction sites for insertional inactivation of the drug markeras follows: pVT63—ApR (HincII, PstI, ScaI), KmR (ClaI, HindIII, NruI,SmaI, XhoI); pVT64—ApR (HincII, PstI, ScaI, SspI) , SpR; pVT65—ApR(HincII, PstI, ScaI, PvuI, SspI), CmR (BalI, NcoI); pVT66—ApR (HincII,PstI, ScaI, PvuI) , CmR (SmaI).pACYC177, pACYC184, pSU2718, pSU2719 are improved shuttle vectors for H.influenzae and E. coli based on p15A (Chandler, 1991, Plasmid25:221-224), have the p15A ori, and were compatible with a plasmidcontaining the RSF0885 origin of replication. Additionally, each plasmidhas multiple cloning sites restriction sites and drug markers asfollows: pACYC177—ApR, KmR (Accession No. X06402); pACYC184—CmR, TcR(Accession No. X06403); pSU2718—CmR and polycloning site from pUC18(Accession No. M64731); and pSU2719—CmR and polycloning site from pUC19(Accession No.M64732).PQL1 is an improved shuttle vector for use in H. influenzae and E. colicontaining both the pMB1 ori and P15a ori, KmR which is flanked by H.influenzae uptake sequences, a multiple cloning site containing a uniqueBamHI and SmaI restriction sites, and which is particularly suited foranalyzing H. influenzae promoter strength in H. influenzae (Heidecker etal., 1994, Gene 150:141-144).

In cloning the recombinant DNA molecule containing the encoding sequenceinto a plasmid vector, one skilled in the art will appreciate that thechoice of restriction enzymes for digesting both the recombinant DNAmolecule and the plasmid to result in compatible ends for ligationdepends on the unique restriction enzyme sites at the ends of therecombinant DNA molecule, whether occurring naturally or engineered suchas during enzymatic amplification; one or more unique restriction enzymesites within the plasmid vector; whether insertion into the plasmidvector will assist in the selection process (See, e.g., pVT66); andwhether a plasmid-derived promoter is used solely, or in addition to thepromoter(s) of the encoding sequences, to drive expression from therecombinant DNA molecule. Selection and screening of transformed H.influenzae htrB mutants may be accomplished by methods known in the artincluding detecting the expression of a marker gene (e.g., drugresistance marker) present in the plasmid, and immunodetection of theexpressed and displayed heterologous bacterial antigen. While thisaspect of the embodiment illustrates that the recombinant DNA moleculecontaining the encoding sequence can be inserted into a plasmid andexpressed in H. influenzae htrB mutants, it will be appreciated by thoseskilled in the art that vectors other than plasmids, can be usedincluding, but not limited to, bacteriophage vectors.

Successful expression of the at least one heterologous bacterial antigenrequires that either the recombinant DNA molecule comprising theencoding sequence, or the vector itself, contain the necessary controlelements for transcription and translation which is compatible with, andrecognized by the particular host system used for expression. Usingmethods known in the art of molecular biology, including methodsdescribed above, various promoters and enhancers can be incorporatedinto the vector or the recombinant DNA molecule containing the encodingsequence to increase the expression of the heterologous bacterialantigen, provided that the increased expression of the heterologousbacterial antigen(s) is compatible with (for example, non-toxic to) thehtrB mutant. As referred to herein, the encoding sequence can containDNA encoding more than one heterologous bacterial antigen, and mayinclude viral and/or fungal antigen-encoding sequences, to create amultivalent antigen for use as an improved vaccine composition.

The selection of the promoter will depend on the expression system used.For example, a preferred promoter in an H. influenzae expression systemmay be the P2 or P6 promoter operatively linked to the encodingsequence. Promoters vary in strength, i.e. ability to facilitatetranscription. Generally, for the purpose of expressing a cloned gene,it is desirable to use a strong promoter in order to obtain a high levelof transcription of the gene and expression into gene product. Forexample, bacterial, phage, or plasmid promoters known in the art fromwhich a high level of transcription has been observed in a host cellsystem comprising E. coli include the lac promoter, trp promoter, recApromoter, ribosomal RNA promoter, the P_(R) and P_(L) promoters, lacUV5,ompF, bla, lpp, and the like, may be used to provide transcription ofthe inserted encoding sequence.

Other control elements for efficient gene transcription or messagetranslation include enhancers, and regulatory signals. Enhancersequences are DNA elements that appear to increase transcriptionalefficiency in a manner relatively independent of their position andorientation with respect to a nearby gene. Thus, depending on the hostcell expression vector system used, an enhancer may be placed eitherupstream or downstream from the encoding sequence to increasetranscriptional efficiency. These or other regulatory sites, such astranscription or translation initiation signals, can be used to regulatethe expression of the encoding sequence. Such regulatory elements may beinserted into the recombinant DNA molecule containing the encodingsequence, or nearby vector DNA sequences using recombinant DNA methodsdescribed herein, and known to those skilled in the art, for insertionof DNA sequences.

Accordingly, a recombinant DNA molecule containing an encoding sequence,can be ligated into an expression vector at a specific site in relationto the vector's promoter, control, and regulatory elements so that whenthe recombinant vector is introduced into the htrB mutant, theheterologous bacterial antigen can be expressed in the host cell. Therecombinant vector is then introduced into the htrB mutant, and thetransformed htrB mutants are selected, and screened for those cellscontaining the recombinant vector. Selection and screening may beaccomplished by methods known in the art, and depending on the vectorand expression system used.

The introduction of a recombinant DNA molecule containing the encodingsequence (including an expression vector or plasmid containing the same)into H. influenzae htrB mutants can be accomplished in any one of threeprocesses: a natural genetic transformation process; transformation ofcompetent bacterial cells; and electroporation of non-competentbacterial cells.

Natural Transformation Process

The natural genetic transformation process of H. influenzae involveslinearized DNA binding, uptake via one or more uptake sequences,translocation, and recombination. Thus, one mechanism to introduce arecombinant DNA molecule containing the encoding sequence to beexpressed into at least one heterologous bacterial antigen, is totransform the host H. influenzae with linearized recombinant DNAmolecule containing the encoding sequence; or a linearized vector havinginserted into it the recombinant DNA molecule containing the encodingsequence to be expressed. In this natural process, when the linearizedDNA is translocated intracellularly, one of the translocated strands ofDNA is apparently degraded by exonuclease activity (Barany et al., 1983,Proc. Natl. Acad. Sci. USA 80:7274-7278). If the translocated strandlacks homology sufficient for recombination into the H. influenzaechromosome, the translocated strand becomes susceptible to furtherdegradation (Pifer et al., 1985, Proc. Natl. Acad. Sci. USA82:3731-3735). Using methods known in the art (e.g., Barany et al.,1983, supra; herein incorporated by reference), linearized DNAcontaining the encoding sequence can be introduced into H. influenzaehtrB mutants. Since the encoding sequence can be flanked by H.influenzae sequences, to increase the likelihood of recombination of theencoding sequence into the H. influenzae htrB mutants, genome is likelyto occur.

Transformation of Competent Bacterial Cells

Another mechanism to introduce a recombinant DNA molecule containing theencoding sequence to be expressed into at least one heterologousbacterial antigen, is to transform competent host H. influenzae htrBmutants with a circular vector, such as a plasmid, having inserted intoit the recombinant DNA molecule containing the encoding sequence to beexpressed. Competence of H. influenzae develops best under conditions inwhich the bacterial cell duplication is inhibited, such as a temporaryshift to anaerobic conditions, by physiological change occurring duringlate-log phase growth, and transfer of cells into nutrient-poor,chemically-defined medium. Such defined media for the development ofcompetence of H. influenzae has been previously described in detail(Herriott et al., 1970, J. Bacteriol. 101:517-524; herein incorporatedby reference). It appears that only a short time after enteringcompetent H.influenzae, a plasmid containing sequences homologous to thebacterial chromosome can insert its homologous sequence (such as theencoding sequence flanked by H. influenzae sequences) into thechromosome via recombination (Setlow et al., 1981, supra). forexpression. Thus, in this embodiment, a plasmid containing the encodingsequence which is capable of being transformed into competent H.influenzae htrB mutants is introduced by methods for transformationknown in the art (Karudapuram et al., 1995, J. Bacteriol. 177:3235-3240;Setlow et al., 1981, supra, herein incorporated by reference). Theencoding sequence may then be recombined into the H. influenzae htrBmutants' genome where it is expressed under the control of its ownpromoter or an H. influenzae promoter near the site of insertion. Suchtransformation is reported to be at a relatively high frequency(McCarthy and Cox, 1986, J. Bacteriol., 168:186-191).

Alternatively, transformation of competent H. influenzae htrB mutants bya circular plasmid with the appropriate origin(s) of replication andcontaining the encoding sequence may result in plasmid establishment;i.e., a plasmid coexisting as an extrachromosomal element withoutrecombination. Examples of such plasmids have been described above.Thus, in this variation of the embodiment, a plasmid containing theencoding sequence which is capable of being transformed into, andestablished in, competent H. influenzae htrB mutants is introduced bymethods for transformation known in the art. The encoding sequence isthen expressed from the plasmid under the control of its own promoter ora promoter within the vector.

Electroporation of Non-Competent Bacterial Cells

Yet another mechanism to introduce a recombinant DNA molecule containingthe encoding sequence to be expressed into at least one heterologousbacterial antigens, is to introduce a circular vector, such as a plasmidhaving inserted into it the recombinant DNA molecule containing theencoding sequence to be expressed, into non-competent host H. influenzaehtrB mutants by electroporation. Electroporation has been used toefficiently introduce plasmid DNA into bacteria. However, optimalconditions may differ depending on the host cell used. Optimalconditions have been described for electroporating plasmid DNA into H.influenzae (Mitchell et al., 1991, Nucl. Acids Res. 19:3625-3628; hereinincorporated by reference). It was found that electroporation of plasmidinto H. influenza made competent by defined, nutrient poor media wasseveral orders of magnitude less efficient than electroporation intonon-competent H. influenzae. Thus, in this variation of the embodiment,it would be preferred that a plasmid containing the encoding sequence iselectroporated into non-competent H. influenzae htrB mutants. Theplasmid is capable of being established in H. influenzae htrB mutants,or is degraded after the encoding sequence has recombined into the H.influenzae htrB mutants, genome. In either case, the encoding sequenceis under the control of its own promoter; or a promoter within thevector or genome, respectively.

EXAMPLE 6 Neisserial htrB Mutants as Immunogens

In another embodiment, the htrB mutant is a Neisserial htrB mutantselected from the group including Neisseria gonorrhoeae, and Neisseriameningitidis N. gonorrhoeae is a gram-negative bacterial pathogencausing the sexually transmitted disease gonorrhea, which subsequentlycan lead to pelvic inflammatory disease in females. N. meningitidis is agram-negative bacterial pathogen which can cause a variety of clinicalinfections including bacteremia, septicemia, meningitis, and pneumonia.Alterations in the terminal glycosylation of the LOS of Neisseria arebelieved correlate with serum sensitivity and serum resistance of theorganism. Further, protective bactericidal antibody is directed againsttype-specific antigens of N. meningitidis, wherein the type-specificantigens have been identified as outer membrane proteins, or LOS, orboth.

Using the methods according to the present invention, as illustrated inExamples 1-3 and 10, htrB mutants of a Neisserial species can beproduced and identified. One skilled in the art, using the htrB gene ofH. influenzae, can isolate the htrB gene of the Neisserial species, andproduce a mutated htrB gene (unable to encode functional HtrB) usingtransposon mutagenesis with subsequent recombination resulting in aNeisserial htrB mutant lacking one or more secondary acyl chains.Alternatively, there may be sufficient homology between Neisseria andHaemophilus to use plasmids pB28 and pB29, each with a mini-Tn3transposon containing the chloramphenicol acetyltransferase (CAT) geneinserted into the htrB open reading frame at a different location, totransform the Neisserial species for recombination of the mutant htrBgene into the Neisserial htrB gene. Neisserial transformants are thenselected for by growth in the presence of chloramphenicol (1.5 μg/ml),resulting in identification of Neisserial htrB mutant strains. Locationsof the mTn3 insertion in the chromosomes of the Neisserial htrB mutantsmay be confirmed by genomic Southern hybridization using a probecontaining htrB sequences. The resultant Neisserial htrB mutants canthen be tested for substantially reduced toxicity using assays describedby those skilled in the art for measuring the toxic effects induced byendotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from a Neisserial htrB mutant can beused in a vaccine formulation in inducing immunity against the wild typestrains of Neisserial pathogens. The htrB mutant LOS may be isolated bya method known to those skilled in the art for isolating LOS. The htrBmutant LOS may be used in a vaccine formulation containing one or moreagents selected from the group consisting of a pharmaceuticallyacceptable carrier (e.g., a physiological solution), an adjuvant, or acarrier protein.

Alternatively, Neisserial htrB mutants can be used in a live bacterialvaccine preparation, in an inactivated bacterial vaccine preparation,and can be genetically engineered to express at least one heterologousbacterial antigen in a multivalent vaccine preparation. Regarding thelatter aspect, plasmids useful for cloning of and expression fromrecombinant DNA molecules into Neisserial species are known to thoseskilled in the art, including:

pLES2 confers ampicillin resistance, is a shuttle vector functional inboth E. coli and N. gonorrhoeae, and contains a polylinker withrestriction sites for EcoRI, SmaI, and BamHI (Stein et al., 1983, Gene25:241-247). Neisserial species also contain a natural transformationprocess (Rudel et al., 1995, Proc Natl Acad Sci USA 92:7896-90; Goodmanet al., 1991, J Bacteriol 173:5921-5923); and can also be made competentor be electroporated using techniques known to those skilled in the art.

EXAMPLE 7 Haemophilus ducreyi htrB Mutants as Immunogens

In another embodiment, the mutant is a H. ducreyi htrB mutant. H.ducreyi is a gram-negative bacterial pathogen causing a genital ulcerdisease, chancroid. Using the methods according to the presentinvention, as illustrated in Examples 1-3 and 10, H. ducreyi htrBmutants can be produced and identified. One skilled in the art, usingthe htrB gene of H. influenzae, can isolate the htrB gene of H. ducreyi,and produce a mutated htrB gene (unable to encode functional HtrB) usingtransposon mutagenesis with subsequent recombination resulting in an H.ducreyi htrB mutant lacking one or more secondary acyl chains.Alternatively, there is likely sufficient homology between H. ducreyiand H. influenzae to use plasmids pB28 and pB29, each with a mini-Tn3transposon containing the chloramphenicol acetyltransferase (CAT) geneinserted into the htrB open reading frame at a different location, totransform H. ducreyi for recombination of the mutant htrB gene into theH. ducreyi htrB gene. H. ducreyi transformants are then selected for bygrowth in the presence of chloramphenicol (1.5 μg/ml), resulting inidentification of H. ducreyi htrB mutant strains. Locations of the mTn3insertion in the chromosomes of the H. ducreyi htrB mutants may beconfirmed by genomic Southern hybridization using a probe containinghtrB sequences. The resultant H. ducreyi htrB mutants can then be testedfor substantially reduced toxicity using assays described by thoseskilled in the art for measuring the toxic effects induced by endotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from an H. ducreyi htrB mutant can beused in a vaccine formulation in inducing immunity against the wild typestrains of H. ducreyi. The htrB mutant LOS may be isolated by a methodknown to those skilled in the art for isolating LOS. The htrB mutant LOSmay be used in a vaccine formulation containing one or more agentsselected from the group consisting of a pharmaceutically acceptablecarrier (e.g., a physiological solution), an adjuvant, or a carrierprotein.

Alternatively, H. ducreyi htrB mutants can be used in a live bacterialvaccine preparation, in an inactivated bacterial vaccine preparation,and can be genetically engineered to express at least one heterologousbacterial antigen in a multivalent vaccine preparation. Regarding thelatter aspect, plasmids useful for cloning of and expression fromrecombinant DNA molecules into Haemophilus species are known to thoseskilled in the art, as disclosed in Example 5; and can also be madecompetent or be electroporated using techniques known to those skilledin the art, as disclosed in Example 5.

EXAMPLE 8 Campylobacter jejuni htrB Mutants as Immunogens

In another embodiment, the mutant is a C. jejuni htrB mutant.Campylobacter jejuni is a gram-negative bacterial pathogen causing humanenteritis. Infection by C. jejuni has also been associated with theonset of neurologic disorders such as Guillian-Barré syndrome. C. jejunihtrB mutants can be produced and identified using the methods accordingto the present invention, as illustrated in Examples 1-3 and 10. Oneskilled in the art, using the htrB gene of H. influenzae, can isolatethe htrB gene of C. jejuni, and produce a mutated htrB gene (unable toencode functional HtrB) using transposon mutagenesis with subsequentrecombination resulting in an C. jejuni htrB mutant lacking one or moresecondary acyl chains. Alternatively, there may be sufficient homologybetween C. jejuni and H. influenzae to use plasmids pB2B and pB29, eachwith a mini-Tn3 transposon containing the chloramphenicolacetyltransferase (CAT) gene inserted into the htrB open reading frameat a different location, to transform C. jejuni for recombination of themutant htrB gene into the C. jejuni htrB gene. C. jejuni transformantsare then selected for by growth in the presence of chloramphenicol (1.5μg/ml), resulting in identification of C. jejuni htrB mutant strains.Locations of the mTn3 insertion in the chromosomes of the C. jejuni htrBmutants may be confirmed by genomic Southern hybridization using a probecontaining htrB sequences. The resultant C. jejuni htrB mutants can thenbe tested for substantially reduced toxicity using assays described bythose skilled in the art for measuring the toxic effects induced byendotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from a C. jejuni htrB mutant can beused in a vaccine formulation in inducing immunity against the wild typestrains of C. jejuni. The htrB mutant LPS may be isolated by a methodknown to those skilled in the art for isolating LPS. The htrB mutant LPSmay be used in a vaccine formulation containing one or more agentsselected from the group consisting of a pharmaceutically acceptablecarrier (e.g., a physiological solution), an adjuvant, or a carrierprotein.

Alternatively, C. jejuni htrB mutants can be used in a live bacterialvaccine preparation, in an inactivated bacterial vaccine preparation,and can be genetically engineered to express at least one heterologousbacterial antigen in a multivalent vaccine preparation. Regarding thelatter aspect, plasmids useful for cloning of and expression fromrecombinant DNA molecules into C. jejuni are known to those skilled inthe art, and includes:

pUA466 confers tetracycline resistance, and contains an unique AvaI siteand AvaII site (Taylor, 1986, J Bacteriol 165:1037-39).C. jejuni can also be made competent or be electroporated usingtechniques known to those skilled in the art.

EXAMPLE 9 Moraxella catarrhalis htrB Mutants as Immunogens

In another embodiment, the mutant is a M. catarrhalis htrB mutant.Moraxella catarrhalis is a gram-negative bacterial pathogen causingotitis media in children; sinusitis and conjunctivitis in children andadults; and lower respiratory tract infections, septicemia, andmeningitis in immunocompromised hosts. M. catarrhalis htrB mutants canbe produced and identified using the methods according to the presentinvention, as illustrated in Examples 1-3 and 10. One skilled in theart, using the htrB gene of H. influenzae, can isolate the htrB gene ofM. catarrhalis, and produce a mutated htrB gene (unable to encodefunctional HtrB) using transposon mutagenesis with subsequentrecombination resulting in an M. catarrhalis htrB mutant lacking one ormore secondary acyl chains. Alternatively, there may be sufficienthomology between M. catarrhalis and H. influenzae to use plasmids pB28and pB29, each with a mini-Tn3 transposon containing the chloramphenicolacetyltransferase (CAT) gene inserted into the htrB open reading frameat a different location, to transform M. catarrhalis for recombinationof the mutant htrB gene into the M. catarrhalis htrB gene. M.catarrhalis transformants are then selected for by growth in thepresence of chloramphenicol (1.5 μg/ml), resulting in identification ofM. catarrhalis htrB mutant strains. Locations of the mTn3 insertion inthe chromosomes of the M. catarrhalis htrB mutants may be confirmed bygenomic Southern hybridization using a probe containing htrB sequences.The resultant M. catarrhalis htrB mutants can then be tested forsubstantially reduced toxicity using assays described by those skilledin the art for measuring the toxic effects induced by endotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from a M. catarrhalis htrB mutant canbe used in a vaccine formulation in inducing immunity against the wildtype strains of M. catarrhalis. The htrB mutant LOS may be isolated by amethod known to those skilled in the art for isolating LPS. The htrBmutant LOS may be used in a vaccine formulation containing one or moreagents selected from the group consisting of a pharmaceuticallyacceptable carrier (e.g., a physiological solution), an adjuvant, or acarrier protein.

Alternatively, M. catarrhalis htrB mutants can be used in a livebacterial vaccine preparation, in an inactivated bacterial vaccinepreparation, and can be genetically engineered to express at least oneheterologous bacterial antigen in a multivalent vaccine preparation.Regarding the latter aspect, plasmids useful for cloning of andexpression from recombinant DNA molecules into M. catarrhalis are knownto those skilled in the art. M. catarrhalis contains a naturaltransformation process (Juni, 1977, J Clin Microbiol 5:227-35) and canalso be made competent or be electroporated using techniques known tothose skilled in the art.

EXAMPLE 10 Salmonella htrB Mutants as Immunogens

In another embodiment, the mutant is a Salmonella htrB mutant.Salmonella species comprise gram-negative bacteria that can cause avariety of clinical illnesses in humans and animals. For example, S.typhi is the causative agent of typhoid fever in humans. S. paratyphi isa causative organism of a fever known as salmonella fever in humans.Salmonellosis, a gastroenteritis in humans, can be caused by variousspecies in the genus Salmonella (typhimurium, newport, heidelberg, andenteritidis). Salmonella htrB mutants can be produced and identified.One skilled in the art, using the htrB gene of a gram-negative bacterialpathogen, can produce a mutated htrB gene (unable to encode functionalHtrB) using transposon mutagenesis and subsequent recombination,ultimately resulting in an Salmonella htrB mutant having a modificationin one or more secondary acyl chains. The resultant Salmonella htrBmutants can then be tested for substantially reduced toxicity usingassays described by those skilled in the art for measuring the toxiceffects induced by endotoxin.

To illustrate this embodiment, and using methods similar to those inExample 1 herein, mutagenesis of the htrB gene was carried out byshuttle mutagenesis by mini-Tn10 (conferring tetracycline resistance)used as an insertion sequence to mutate the htrB gene. The htrB:Tn10 wasthen transfered from E. coli to a virulent S. typhimurium bytransduction. Using methods previously described (Masters, 1996, in E.coli and Salmonella Cellular and Molecular Biology, vol. 2, 2nd edition,p. 2421, ASM Press), a r⁻m⁺ galE mutS reCD S. typhimurium (SL5283) wassequentially transduced with MST3488 (recD542:Tn10d which conferschloramphenicol resistance (cm^(r))) via Salmonella phage P22 resultingin a r⁻m⁺ galE mutS recD cm^(r) S. typhimurium (“MGS-1”) , and then withMST3063 (mutS:Tn10 which confers tertracycline resistant (tet^(r)))resulting in a r⁻m⁺ galE mutS recD cm^(r) tet^(r) S. typhimurium(“MS-3”). S. typhimurium MGS-3 was cured of Tn10 by selection fortetracycline sensitivity on media using methods previously described(Bochner et al., 1990, J. Bacteriol. 143:926-933) resulting in a r⁻m⁺galE mutS reCD cm^(r) S. typhimurium (“MGS-7”). For confirmationpurposes, it was shown that S. typhimurium MGS-7 showed the sameresponse to ultraviolet light as the parental strain MGS-3.

An E. coli strain (“MLK217”) containing the htrB:mini Tn10 was used totransfer the htrB:Tn10 by transduction into S. typhimurium MGS-7 viacoliphage P1 according to methods previously described (Masters, 1996,supra), and selected for by growth at 30° C. on media plates containingtetracycline. The result of the transduction, and after reisolation fortetracycline-resistant clones, was the creation of a r⁻m⁺ galE mutS recDhtrB:mini Tn10 cm^(r) tet^(r) S. typhimurium (“MGS-23”). S. typhimuriumMS-23 was tested for one or more of the phenotypic properties associatedwith htrB mutation, namely (1) temperature sensitivity; (2)filamentation and bulging at non-permissive temperatures; and (3)deoxycholate resistance. The results of the phenotypic analysisindicated that MGS-23 carried the miniTn 10 element inserted within theS. typhimurium htrB gene because MGS-23 was able to grow at 30° C. butnot at 37° C.; formed many filamentous forms when shifted tonon-permissive temperature; and showed resistance to higherconcentrations of deoxycholate (7.5% to 10%) than the isogenic parent(2.5%). The mutation of the htrB was further confirmed by analysis usingpolymerase chain reaction.

A virulent S. typhimurium strain (SL1344) was transduced to htrB:Tn10from S. typhimurium MGS-23 via Salmonella phage P22 and selection at 30°C. on media plates containing tetracycline. After isolation, resultanttetracycline resistant clones having the same phenotype as MGS-23 werefurther analyzed. One such clone, MGS-31, was shown to have a mutatedhtrB gene, by complementing the clone using a plasmid with a wild typehtrB gene (Karow et al., 1991, J. Bacteriol. 173:741-50; Karow et al.,1991, Mol. Microbiol. 5:2285-2292) thereby returning the clone to thewild type phenotype of normal growth, normal cell morphology,deoxycholate sensitivity at 37° C., and wild type virulence.

Endotoxin Characteristics

Mass spectrometry was used to analyze the lipid A according to themethods in Example 2 herein. More specifically, lipid A from S.typhimurium htrB mutant LPS and from wild type S. typhimurium LPS wereeach analyzed by liquid secondary ion mass spectrometry (LSIMS) in thenegative ion mode to provide a spectrum of molecular ions for thedifferent components lipid A. The chemical analysis of the lipid A ofthe S. typhimurium htrB mutant indicated that the modifications in thelipid A structure that occurred were similar, but not identical, tomodifications in the lipid A structure seen in H. influenzae htrBmutants. In the wild type S. typhimurium lipid A contains either six(hexaacyl) or seven (heptaacyl) fatty acid substitutions from thediglucosamine backbone (FIG. 7). In the wild type strain, on glucosamineII, the 3′ substitution on the N-linked C14 fatty acid (hexaacyl orheptaacyl) is a C12 fatty acid. In contrast, and as shown in FIG. 7, theC12 fatty acid is replaced with a C16 fatty acid. These results indicatethat the S. typhimurium htrB gene encodes an acyltransferase responsiblefor placing the C12 fatty acid at the 3′ position on the N-linked C14fatty acid. Mutation of the S. typhimurium htrB gene results in thefunctional induction of another acyltransferase which places a C16 fattyacid at the 3′ position on the N-linked C14 fatty acid. It is known tothose skilled in the art, that lipid A is crucial for the survival of agram-negative organism, and for the proper organization of its outermembrane. Thus, and as related to virulence and toxicity of theorganism, the effects of the htrB gene mutation in S. typhimurium wasanalyzed.

Endotoxin Toxicity

A mouse model system that is used by those skilled in the art asrelevant to human disease, is the D-galactosamine model. In theD-galactosamine model, the sensitivity to LPS is increased by exposureto D-galactosamine (Galanos et al., 1986, Infect. Immun. 51:891-896)thereby achieving the same lethality and TNF induction with low doses ofLPS, i.e. with levels of endotoxin commensurate with those identified inthe blood of septic patients. Thus, D-galactosamine-treated mice exposedto LPS is a standard animal model system accepted by those skilled inthe art as relevant to endotoxic shock in humans. In this model, groupsof 4 mice were treated with D-galactosamine (8 mg) simultaneously withthe administration of the dosage of the LPS to be tested. Groups of 4mice each were injected with either 0.001 μg, 0.01 μg, 0.1 μg, 1 μg or10 μg of the purified LPS to be tested and the number of mice survivingthe challenge at each dose were checked every 24 hours for 5 days afterthe injection. The LD₅₀ (lethal dose where 50% of the mice are killed)is then calculated. The purified LPS to be separately tested includedLPS from the wild type virulent S. typhimurium strain 1344; and the S.typhimurium htrB mutant (MGS-31). The results show that the LD₅₀ formice injected with LPS from S. typhimurium strain 1344 is 0.01 μg. Incontrast, the LD₅₀ for mice injected with LPS from S. typhimurium htrBmutant MGS-31 is 0.1 μg. Thus, the lipid A from the S. typhimurium htrBmutant is at least 10 fold less toxic than the lipid A of the wild typestrain.

Virulence

Since mice are naturally susceptible to infection by S. typhimurium,like humans, a second mouse model was used to assess the effects of thehtrB mutation on virulence of S. typhimurium. Typically, fromapproximately 50 cfu to 100 cfu will kill 50 to 100% of the miceinjected. The strains used included S. typhimurium strain 1344; S.typhimurium htrB mutant (MGS-31); and the S. typhimurium htrB mutantwhich was complemented by the plasmid containing an intact htrB gene(MGS-43). The respective organisms were injected intraperitoneally in adosage ranging from 5×10¹ to 5×10⁷ cfu and watched over 5 days.Generally, 100% of the animals who will die from bacteremia, do sowithin that period. As may be expected, the LD, for the virulent S.typhimurium strain 1344 was less than 5×10¹ cfu. Likewise, the LD₅₀ forthe S. typhimurium htrB mutant which was complemented with the intacthtrB gene, MGS-43, also was less than 5×10¹ cfu. In contrast, the LD₅₀for the S. typhimurium htrB mutant MGS-31 was 9.7×10⁶ cfu, anapproximately 2×10⁵ reduction in virulence compared to the wild typevirulent strain. S. typhimurium htrB mutant growth in vivo in mice wasconfirmed by culturing and assaying liver and spleen for bacterialcounts. The results suggest that the htrB mutation in Salmonella has amore profound effect on virulence factors than just a modification ofthe LPS.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from a Salmonella htrB mutant can beused in a vaccine formulation in inducing immunity against the wild typestrains of the Salmonella species. The htrB mutant LPS may be isolatedby a method known to those skilled in the art for isolating LPS. ThehtrB mutant LPS may be used in a vaccine formulation containing one ormore agents selected from the group consisting of a pharmaceuticallyacceptable carrier (e.g., a physiological solution), an adjuvant, or acarrier protein.

Alternatively, Salmonella htrB mutants can be used in a live bacterialvaccine preparation, in an inactivated bacterial vaccine preparation,and can be genetically engineered to express at least one heterologousbacterial antigen in a multivalent vaccine preparation. Regarding thelatter aspect, plasmids useful for cloning of and expression fromrecombinant DNA molecules into Salmonella are known to those skilled inthe art, and includes:

pYA260 containing lacZ cloned into a trc promoter; andpJW270 conferring tetracycline resistance and containing lacI (Ervin etal., 1993 Microb Pathogen 15:93-101).pB7 confers kanamycin and chloramphenicol resistance, and contains acloning Bite flanked by a BalI site and a HindIII site (Purcell et al.,1983, Infect Immun 39:1122-1127).pACK5 contains the replicon of PAC1 from Acetobacter pasteurianus andconfers kanamycin resistance (Grones et al., 1995, Biochem Biophys ResCommun 206:942-947).pVAC468 is a suicide vector for chromosomal insertion of heterologousantigens into Salmonella and contains a polylinker having the followingrestriction sites: ClaI, EcoRV, XhoI, SacI, SalI, SmaI, XbaI, and BglII(Hohmann et al., 1995, Proc Natl Acad Sci USA 92:2904-2908). Alsodisclosed is a bacteriophage system, a ‘chromosomal expression vector’for inserting genes encoding foreign antigens into the chromosome ofSalmonella, which uses a defective transposable element carried onbacteriophage lambda (Flynn et al., 1990, Mol Microb 4:2111-2118).Salmonella can also be made competent (see for example, Purcell et al.,1983, supra) or be electroporated using techniques known to thoseskilled in the art (see for example, Grones et al., 1995, supra; Coulsonet al., 1994, supra).

EXAMPLE 11 Shigella htrB Mutants as Immunogens

In another embodiment, the mutant is a Shigella species htrB mutant.Members of the genus Shigella are gram-negative bacteria which causediseases such as dysentery (pathogenic species include dysenteriae,sonnei, and flexneri) primarily in humans. Shigella htrB mutants can beproduced and identified using the methods according to the presentinvention, as illustrated in Examples 1-3 and 10. One skilled in theart, using the htrB gene of H. influenzae, can isolate the htrB gene ofShigella, and produce a mutated htrB gene (unable to encode functionalHtrB) using transposon mutagenesis with subsequent recombinationresulting in an Shigella htrB mutant lacking one or more secondary acylchains. Alternatively, there may be sufficient homology between Shigellaand H. influenzae to use plasmids pB28 and pB29, each with a mini-Tn3transposon containing the chloramphenicol acetyl-transferase (CAT) geneinserted into the htrB open reading frame at a different location, totransform Shigella for recombination of the mutant htrB gene into theShigella htrB gene. Shigella transformants are then selected for bygrowth in the presence of chloramphenicol (1.5 μg/ml), resulting inidentification of Shigella htrB mutant strains. Locations of the mTn3insertion in the chromosomes of the Shigella htrB mutants may beconfirmed by genomic Southern hybridization using a probe containinghtrB sequences. The resultant Shigella htrB mutants can then be testedfor substantially reduced toxicity using assays described by thoseskilled in the art for measuring the toxic effects induced by endotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from an htrB mutant made from apathogenic Shigella species can be used in a vaccine formulation ininducing immunity against the wild type strains of Shigella. The htrBmutant LPS may be isolated by a method known to those skilled in the artfor isolating LPS. The htrB mutant LPS may be used in a vaccineformulation containing one or more agents selected from the groupconsisting of a pharmaceutically acceptable carrier (e.g., aphysiological solution), an adjuvant, or a carrier protein.

Alternatively, Shigella htrB mutants can be used in a live bacterialvaccine preparation, in an inactivated bacterial vaccine preparation,and can be genetically engineered to express at least one heterologousbacterial antigen in a multivalent vaccine preparation. Regarding thelatter aspect, plasmids useful for cloning of and expression fromrecombinant DNA molecules into Shigella are known to those skilled inthe art, and includes:

pACK5 contains the replicon of pAC1 from Acetobacter pasteurianus andconfers kanamycin resistance (Grones et al., 1995, supra).Shigella can also be made competent or be electroporated usingtechniques known to those skilled in the art.

EXAMPLE 12 Pseudomonas aeruginosa htrB Mutants as Immunogens

In another embodiment, the mutant is a Pseudomonas aeruginosa htrBmutant. Pseudomonas aeruginosa is a gram-negative bacterial pathogenwhich cause diseases such as respiratory tract infections and sepsis,particularly in immocompromised patients. Other pathogenic species forhumans and animals include pseudomallei, and mallei. Mass spectrometryand nuclear magnetic resonance spectroscopy were used to determine thestructure of lipid A of Pseudomonas aeruginosa LPS. The structure of P.aeruginosa lipid A was found to be the same as Enterobacterial lipid A:a backbone of a glucosamine disaccharide which is eithermono-phosphorylated or diphosphorylated (positions 1 and 4′); and whichcarries several molecules of ester- and amide-bound fatty acids. Inaddition to the hexaacyl and pentaacyl lipid A species, a tetraacylspecies was identified (Karunaratne et al., 1992, Arch Biochem Biophys299:368-76).

Pseudomonas htrB mutants (e.g., P. aeruginosa) can be produced andidentified using the methods according to the present invention, asillustrated in Examples 1-3 and 10. One skilled in the art, using thehtrB gene of H. influenzae, can isolate the htrB gene of Pseudomonasaeruginosa, and produce a mutated htrB gene (unable to encode functionalHtrB) using transposon mutagenesis with subsequent recombinationresulting in a P. aeruginosa htrB mutant lacking one or more secondaryacyl chains. Alternatively, there may be sufficient homology between P.aeruginosa and H. influenzae to use plasmids pB28 and pB29, each with amini-Tn3 transposon containing the chloramphenicol acetyltransferase(CAT) gene inserted into the htrB open reading frame at a differentlocation, to transform P. aeruginosa for recombination of the mutanthtrB gene into the P. aeruginosa htrB gene. P. aeruginosa transformantsare then selected for by growth in the presence of chloramphenicol (1.5μg/ml), resulting in identification of P. aeruginosa htrB mutantstrains. Locations of the mTn3 insertion in the chromosomes of the P.aeruginosa htrB mutants may be confirmed by genomic Southernhybridization using a probe containing htrB sequences. The resultant P.aeruginosa htrB mutants can then be tested for substantially reducedtoxicity using assays described by those skilled in the art formeasuring the toxic effects induced by endotoxin.

Using the methods according to the present invention, as illustrated inExamples 4 & 5, endotoxin isolated from a P. aeruginosa htrB mutant canbe used in a vaccine formulation in inducing immunity against the wildtype strains of P. aeruginosa. The htrB mutant LPS may be isolated by amethod known to those skilled in the art for isolating LPS. The htrBmutant LPS may be used in a vaccine formulation containing one or moreagents selected from the group consisting of a pharmaceuticallyacceptable carrier (e.g., a physiological solution), an adjuvant, or acarrier protein.

Alternatively, P. aeruginosa htrB mutants can be used in a livebacterial vaccine preparation, in an inactivated bacterial vaccinepreparation, and can be genetically engineered to express at least oneheterologous bacterial antigen in a multivalent vaccine preparation.Regarding the latter aspect, plasmids useful for cloning of andexpression from recombinant DNA molecules into P. aeruginosa are knownto those skilled in the art, and includes:

pPAH121 confers carbenicillin resistance, and contains a unique HpaIrestriction site (Hoyne et al., 1992, J Bacteriol 174:7321-7327.P. aeruginosa can also be made competent (see for example, Hoyne et al.,1992, supra) or be electroporated using techniques known to thoseskilled in the art.

EXAMPLE 13 Multivalent htrB Mutant Vaccine Formulation

In one embodiment according to the present invention, as illustrated inExamples 4 & 5, the htrB mutant is genetically engineered to express oneor more heterologous microbial antigens in producing a multivalentvaccine using methods known to those skilled in the art. In a preferredembodiment, a microbial pathogen may include a respiratory pathogenselected from the group of pathogens, with respective antigens, in Table2.

TABLE 2 PATHOGEN INFECTION/DISEASE PROTEIN ANTIGEN H. influenzae otitismedia, D-15, P1, P6¹ lower respiratory tract Group A pharyngitis, M²Streptococcus rheumatic fever Branhamella otitis media, CD, E³catarrhalis lower respiratory tract Streptococcus pneumonia, otitisautolysin, pneumoniae media, meningitis pneumolysin⁴ Bordetellapertussis filamentous pertussis (whooping cough) hemagglutinin,pertussis toxin, 69 kDa Omp⁵ Pseudomonas respiratory tract Omp OprF,aeruginosa exotoxin A⁶ Legionella pneumonia OmpS, Hsp60⁷ pneumophilaMycoplasma upper and lower P1⁸ pneumoniae respiratory tract Respiratorylower respiratory M2, P, F, G⁹ syncytial virus tract Influenza virusinfluenza HA, M¹⁰ Adenovirus common cold rhinovirus common cold VP1,VP2, VP3¹¹ Parainfluenza common cold HN, F¹² virus Pneumocystispneumonia in AIDS msg¹³ carinii ¹(Flack et al., 1995 Gene 156: 97-99;Panezutti et al., 1993, 61: 1867-1872; Nelson et al., 1988, Rev InfectDiseases 10: S331-336). ²(Pruksakorn et al., 1994, Lancet 344: 639-642;Dole et al., 1993, J Immunol 151: 2188-94). ³(Murphy et al., 1989,Infect Immun 57: 2938-2941; Faden et al., 1992, Infect Immun 60:3824-3829). ⁴(Lock et al., 1992, Microb Pathog 12: 137-143). ⁵(Novotnyet al., 1991, Dev Biol Stand 73: 243-249; Lipscombe et al., 1991, MolMicrobiol 5: 1385-1392; He et al., 1993, Eur J Clin Microbiol Infect Dis12: 690-695). ⁶(Rawling et al., 1995, Infect Immun 63: 38-42; Penningtonet al., 1988, J Hosp Infect 11A: 96-102). ⁷(Weeratna et al., 1994,Infect Immun 62: 3454-3462). ⁸(Jacobs et al., 1990, Infect Immun 58:2464-2469; 1990, J Clin Microbiol 28: 1194-1197). ⁹(Kulkarni et al.,1995, J Virol 69: 1261-1264; Leonov et al., 1994, J Gen Virol 75:1353-1359; Garcia et al., 1993, Virology 195: 239-242; Vaux-Peretz etal., 1992, Vaccine 10: 113-118). ¹⁰(Kaly et al., 1994, Vaccine 12:753-760; Bucher et al., 1980, J Virol 36: 586-590). ¹¹(Francis et al.,1987, J Gen Virol 68: 2687-2691). ¹²(Morein et al., 1983, J Gen Virol64: 1557-1569). ¹³(Garbe et al., 1994, Infect Immun 62: 3092-3101).

In another preferred embodiment, a microbial pathogen may include apathogen causing a sexually transmitted disease selected from the groupof pathogens, with respective antigens, in Table 3.

TABLE 3 PATHOGEN INFECTION/DISEASE PROTEIN ANTIGEN N. gonorrhoeaegonorrhea IgA1 protease¹, PIB², H.8³, Por⁴ Chlamydia nongonococcalMOMP⁵, HSP⁶ trachomatis urethritis ¹(Lomholt et al., 1994, Infect Immun62: 3178-83). ²(Heckels et al., 1990, Vaccine 8: 225-230). ³(Blacker etal., 1985, J Infect Dis 151: 650-657). ⁴(Wetzler et al., 1992, Vaccine8: 225-230). ⁵(Campos et al., 1995, Ophthamol Vis Sci 36: 1477-91;Murdin et al., 1995, Infect Immun 63: 1116-21). ⁶(Taylor et al., 1990,Infect Immun 58: 3061-3).

Tables 2 & 3, and the references footnoted which are herein incorporatedby reference, illustrate various protein antigens, or peptides thereof,viewed by those skilled in the art to be useful as vaccine candidatesagainst the respective microbial pathogen. Typically, the immunopotencyof an epitope, whether from a protein or peptide, of a microbialpathogen is determined by monitoring the immune response of an animalfollowing immunization with the epitope and/or by analyzing humanconvalescent sera in conjunction with pre-immune sera. Thus, one skilledin the art can determine protein or peptide antigens from microbialpathogens which would be desired to include as a heterologous antigen tobe expressed by an htrB mutant according to the present invention. Acorresponding nucleic acid sequence, the encoding sequence, can then bededuced from the amino acid sequence of the protein or peptide antigen,wherein the encoding sequence is introduced into the htrB mutant forexpression.

EXAMPLE 14 Use of htrB Mutants to Generate Antisera

The htrB mutant, or endotoxin purified therefrom, can be used togenerate endotoxin-specific antisera, directed to the particulargram-negative bacterial pathogen, which can be used in an immunoassay todetect the antigen (that particular gram-negative bacterial pathogen),present in the body fluid of an individual suspected of having aninfection caused by that gram-negative bacterial pathogen. The bodyfluid(s) collected for analysis depend on the microorganism to bedetected, the suspected site of infection, and whether the body fluid issuspected of containing the antigen or containing antisera. With thoseconsiderations in mind, the body fluid could include one or more ofsputum, blood, cerebrospinal fluid, lesion exudate, swabbed materialfrom the suspected infection site, and fluids from the upper respiratorytract. Immunoassays for such detection comprises any immunoassay knownin the art including, but not limited to, radioimmunoassay, ELISA,“sandwich” assay, precipitin reaction, agglutination assay, fluorescentimmunoassay, and chemiluminescence-based immunoassay.

Alternatively, where an immunocompromised individual is suffering from apotentially life-threatening infection caused by a particulargram-negative bacterial pathogen, immunization may be passive, i.e.immunization comprising administration of purified human immunoglobulincontaining antibody against an htrB mutant or isolated htrB endotosin ofthat particular gram-negative bacterial pathogen.

It should be understood that while the invention has been described indetail herein, the examples were for illustrative purposes only. Othermodifications of the embodiments of the present invention that areobvious to those skilled in the art of molecular biology, medicaldiagnostics, and related disciplines are intended to be within the scopeof the appended claims.

1. A vaccine formulation comprising an active ingredient selected fromthe group consisting of an htrB mutant of a gram-negative bacterialpathogen, endotoxin isolated from the htrB mutant of said gram-negativebacterial pathogen, endotoxin isolated from the htrB mutant of saidgram-negative bacterial pathogen said endotoxin conjugated to a carrierprotein, and an htrB mutant of said gram-negative bacterial pathogenwhich has been genetically engineered to express at least oneheterologous vaccine antigen; wherein said htrB mutant lacks one or moresecondary acyl chains of lipid A contained in the gram-negativebacterial pathogen resulting in substantially reduced toxicity whencompared to lipid A of the gram-negative bacterial pathogen.
 2. Thevaccine formulation of claim 1, wherein the active ingredient consistsessentially of an htrB mutant of said gram-negative bacterial pathogen.3. The vaccine formulation of claim 1, wherein the active ingredientconsists essentially of endotoxin isolated from the htrB mutant of saidgram-negative bacterial pathogen.
 4. The vaccine formulation of claim 1,wherein the active ingredient consists essentially of endotoxin isolatedfrom the htrB mutant of said gram-negative bacterial pathogen, whereinthe isolated endotoxin is conjugated to a carrier protein.
 5. Thevaccine formulation of claim 1, wherein the active ingredient consistsessentially of an htrB mutant of said gram-negative bacterial pathogenwhich has been genetically engineered to express at least oneheterologous antigen from a microbial pathogen.
 6. The vaccineformulation of claim 1, further comprising a physiological carrier andan adjuvant.
 7. The vaccine formulation of claim 1, wherein thegram-negative bacterial pathogen is a Neisseria, Haemophilus, Moraxella,Campylobacter, Salmonella, Shigella, or Pseudomonas gram-negativebacterial pathogen.
 8. The vaccine formulation of claim 7, wherein thegram-negative bacterial pathogen is Neisseria meningitidis, Neisseriagonorrhoeae, Haemophilus influenzae, Haemophilus ducreyi, Moraxellacatarrhalis, Campylobacter jejuni, Salmonella typhimurium, Shigelladysentariae, or Pseudomonas aeruginosa.
 9. The vaccine formulation ofclaim 8, wherein the gram-negative bacterial pathogen is Haemophilusinfluenzae.
 10. The vaccine formulation of claim 9, wherein thegram-negative bacterial pathogen is non-typeable Haemophilus influenzae.11. The vaccine formulation of claim 10, wherein the endotoxin of thehtrB mutant contains a decreased phosphoethanolamine content and anincreased hexose content in the mutant endotoxin's inner core, and apentaacylated or tetraacylated lipid A lacking one or two secondary acylchains compared to the corresponding wild-type non-typeable Haemophilusinfluenzae hexaacylated endotoxin.
 12. A method for immunizing anindividual to prevent disease caused by a gram-negative bacterialpathogen, the method comprising vaccinating the individual with aprophylactically effective amount of the vaccine formulation of claim 1.13. The method of claim 12, wherein the individual is a human.
 14. Themethod of claim 12, wherein the individual is not a human.
 15. Themethod of claim 12, wherein the vaccine formulation is introduced by aroute of administration selected from the group consisting ofintradermal, intramuscular, intraperitoneal, intravenous, subcutaneous,ocular, intranasal, and oral administration.
 16. The method of claim 12,wherein the vaccine formulation comprises an active ingredientconsisting essentially of an htrB mutant of said gram-negative bacterialpathogen.
 17. The method of claim 12, wherein the vaccine formulationcomprises an active ingredient consisting essentially of endotoxinisolated from the htrB mutant of said gram-negative bacterial pathogen.18. The method of claim 12, wherein the vaccine formulation comprises anactive ingredient consisting essentially of endotoxin isolated from thehtrB mutant of said gram-negative bacterial pathogen, wherein theisolated endotoxin is conjugated to a carrier protein.
 19. The method ofclaim 12, wherein the vaccine formulation comprises an active ingredientconsisting essentially of an htrB mutant of said gram-negative bacterialpathogen which has been genetically engineered to express at least oneheterologous antigen from a microbial pathogen.
 20. The method of claim12, wherein the vaccine formulation further comprises a physiologicalcarrier and an adjuvant.
 21. The method of claim 15, wherein the vaccineformulation is administered orally as an additive to the individual'sfeed.
 22. The method of claim 12, wherein the gram-negative bacterialpathogen is a Neisseria, Haemophilus, Moraxella, Campylobacter,Salmonella, Shigella, or Pseudomonas gram-negative bacterial pathogen.23. The method of claim 22, wherein the gram-negative bacterial pathogenis Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilusinfluenzae, Haemophilus ducreyi, Moraxella catarrhalis, Campylobacterjejuni, Salmonella typhimurium, Shigella dysentariae, or Pseudomonasaeruginosa.
 24. The method of claim 23, wherein the gram-negativebacterial pathogen is Haemophilus influenzae.
 25. The method of claim24, wherein the gram-negative bacterial pathogen is non-typeableHaemophilus influenzae.
 26. The method of claim 24, wherein theendotoxin of the htrB mutant contains a decreased phosphoethanolaminecontent and an increased hexose content in the mutant endotoxin's innercore, and a pentaacylated or tetraacylated lipid A lacking one or twosecondary acyl chains compared to the corresponding wild-typenon-typeable Haemophilus influenzae hexaacylated endotoxin.